DTC 14

Chart - Code 14 Coolant Sensor Circuit (Signal Voltage Low):

Code 14 Coolant Temperature Sensor Circuit (High Temp. Indicated):

CIRCUIT DESCRIPTION
The coolant temperature sensor uses a thermistor to control the signal voltage to the Electronic Control Module (ECM). The ECM applies a voltage on circuit 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage. As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature the voltage will measure about 1.5 to 2.0 volts at the ECM terminal "C16".
Coolant temperature is one of the inputs used to control:
^ Fuel delivery
^ Engine spark timing (EST)
^ Idle Air Controller (IAC)
^ Torque Converter clutch (TCC)
^ Canister purge (CCP)
^ Exhaust Gas Recirculation (EGR)
^ Cooling fan

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Code 14 will set if the signal voltage indicates a coolant temperature above 135° C (275° F) for 3 seconds.
2. This test will determine if circuit 410 is shorted to ground which will cause the conditions for Code 14.

DIAGNOSTIC AIDS
Check harness routing for a potential short to ground in circuit 410. circuit is routed from the ECM to a mini harness, and then to the coolant temperature sensor. The "SCAN" tool displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90° C then stabilize when thermostat opens.

Refer to Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions

NOTES:
^ Verify that engine is not overheating and has not been subjected to conditions which could create an overheating condition (i.e. overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.).

^ The "Temperature To Resistance Value" scale may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.